Conventionally, capacitance sensors have been used for measuring capacitance formed between a workpiece and a distributed electrode of a sensing probe. In such conventional systems, one electrode of the sensor must be electrically involved in the system, which is typically accomplished by mechanically contacting the workpiece to the capacitance senor. In the conventional systems, the workpiece accordingly becomes one electrode of the capacitance electrodes. A disadvantage of these conventional capacitance systems is that the workpiece being sensed is limited to a conductive object, such as a metal object, which is necessary to form one plate of the conventional capacitance sensor. The necessity of using a metal object as the workpiece limits the variety of workpieces that may be sensed because the sensor is directly connected to the workpiece in order to form one plate of the sensor.
Other types of capacitance based sensors rely on physical contact between the probe electrode and the workpiece electrode with a known dielectric intermediary. When these contacting capacitance sensors are used, vibrations of the workpiece may cause the sensors to wear rapidly. As a result, the sensor must be frequently calibrated since the capacitance parameters for the sensor in the workpiece will be altered and differences from the initially calibrated capacitance parameters must be compensated for. Accordingly, such contacting capacitance sensor systems have a reduced accuracy because of frequent replacement and recalibration.
As will be described further hereinbelow with reference to the preferred embodiments, the present invention is directed to a method and a system for imaging desired surfaces of a workpiece by a non-contact capacitance sensor. The non-contacting capacitance sensor of the present invention overcomes the above described disadvantages in both the conventional and contacting capacitance sensor systems and allows a wide variety of workpieces having a significant conductivity or a dielectric constant significantly different from air to be imaged. The novel method and system of the present invention provides a low cost and time efficient imaging system for a high resolution image sensor.